Why Does My Dog... Chase His Tail?

Tail-chasing is a perfectly normal behavior for a playful dog. She’s merely expending excess energy and expressing her desire for exercise and play.

Dogs who chase their tails for fun are enjoying the sensation of free-wheeling, happy playfulness in a prey-centric fashion. Watching a dog chase her tail is undeniably entertaining, but when she does it constantly it can get worrisome. Some
dogs with anal gland problems, flea allergic dermatitis or other medical issues have been known to chase their rear ends. Sometimes — albeit uncommonly — tail-chasing is a sign of obsessive compulsive disorder.

The key to identifying the behavior as OCD is to note whether the
dog can be engaged or distracted while in the throes of a dedicated tail-chasing session. If the dog can't be distracted, speak to your veterinarian. He might even refer you to a veterinary behaviorist.